I think the point is that regardless of "I didn't know it was against the law" excuses, you are likely to still know what you are doing is likely to be with bad intentions regardless of your knowledge of the law.
In this case the cleaners didn't even break in, the door was open. They went in without breaking in, they cleaned. Both these actions done with only good intentions. Therefore I reason out this to be an "anti-crime" as described above.